Condenser



July 13, 1937. 1 G. KETCHAM 2,086,914

CONDENSER K Filed oct. 18, 19:55 3 sheets-sheet 1' wle-y Julv 13, 19x37. L, G, KETCHAM 2,086,914

CONDENSER Filed Oct. 18, 1955 3 Sheets-Sheet 2 8] INVENTOR.

96m ATTORNEYS July 13,

CONDENSER Filed Oct. 18, 19?;55 3 Sheets-Sheec 5 ya 5a INVENTQR.

L? @U2 i Patented July 13, 1937 UNITED STATES PATENT OFFICE CONDENSER Application October 18, 1935, Serial No. 45,584

3 Claims.

This invention relates to improvements in condensers and more particularly to improvements in condensers of the character known to the art as padder or trimmer condensers.

5 -An object of the present invention is to proprovide a condenser which is substantially unaffected by temperature or humidity changes.

Another object of the invention is to provide a condenser having a base so shaped as to contain a cavity for the reception of the condenser elements whereby these elements are \both restricted from undesired movement, and the frangible elements are protected.

Another object of the invention is to provide a condenser Vin which the base is provided with an element receiving cavity, the walls of which are so shaped as to, in conjunction with formations of the elements, definitely align the elements properly.

A further object of the invention is to provide a condenser arrangement wherein the base may be provided with a plurality of cavities for the reception of multiple condenser units, together with means for electrically connecting the adjusting members of the units so that all of the adjusting members can be grounded through a single connection.

A still further object of the invention is to provide a multiple condenser assembly of such character that the units can be independently tuned without causing detuning of the circuits with which the units are associated due tobody capacity of the operator.

Another object of the invention is to provide a multiple condenser assembly of such construction that stray capacities between the multiple condensers are minimized.

In carrying out the foregoing and other objects of the invention, the condenser in unitary or multiple form is made up of a molded base of insulating material, which is substantially nonhygroscopic. This base is provided either with a single cavity or with a plurality or cavities. Each cavity is substantially open ended, being deiined by opposite walls which are so dimensioned as to receive the condenser elements therebetween. The opposite walls are provided with ribs or bosses which cooperate with recesses or notches in the condenser elements to properly align these elements in the cavity. An adjustment screw passes through the base, through the condenser plates and the interposed dielectric strips, into engagement with a relatively heavy pressure plate which serves to compress such of the plates as are normally bowed.;4 I'he major portion 'of each disposed on the condenser plates as to be in staggered relation when the unit is assembled. 1o Since the strips of dielectric material are made of some relatively frangible material, such as mica, etc., the cavity walls serve to protect the overhanging parts of these strips from being frayed or otherwise injured. l5

When the condenser construction is in the nature of a multiple unit assembly, provision is made for grounding the adjustment screws of all of the condensers through a common connection. For this purpose a metallic bar engages 20 each of the adjusting screws in such fashion as to make good electrical connections therewith. This bar in turn can be connected electrically with a grounded part of the chassis or a radio set by means of the same member which is 25 utilized for fastening the assembly to the chassis, or to a shielded can.

Other features, objects and advantages of the invention will become apparent by-reference to the following detailed description read in the 30 light of the accompanying drawings, wherein- Fig. 1 is a plan view of the device embodying the invention.

Fig. 2 is an enlarged section taken substantially on the line 2-2 of Fig. 1. 435

Fig. 3 is an enlarged section taken substantially on the line 3-3 of Fig. 1.

Figs. 4, 5 and 6 are plan views of elements used in the condenser construction.

Fig. 7 is a plan view of a modification of the 40 i invention.

Fig. 8 is a similar view of the opposite side of the same device.

Fig. 9 is a plan view of a further modification of the invention. 45

Fig. 10 is a similar View of the opposite side ofthe same device.

Fig. 1l is a perspective fragmentary view of an assembly utilizing one form of the invention; and 50 Fig. 12 is a section taken substantially on the line l2-I2 of Fig. 11.

Referring now to the drawings, l0 indicates a base member, such base member being composed of some suitable insulating non-hygroscopic ma 55 terial, such as a highly compressed ceramic material, thoroughly impregnated with wax or other moisture repellant. This base lil is provided with an open ended cavity which is defined by the opposite walls il! and l2. apertures Hiare provided on opposite sides of the base for the passage of suitable members for attaching the base in a radio` receiving chassis, or any other suitable location. The base is also provided with an aperture l5 substantially symmetrically located relative to the walls il and and to the open ends ofv the cavity dened by these walls. The surface oi the base member opposite the cavity is provided with a recess as shown clear ly in Fig.

The condenser-elements used in conjunction with this base consists of condenser plates strips oi dielectric material il; a pressure plate ci@ and an adjusting member or screw 2HE. The

' condenser plates, two or more or which may be used in a condenser assembly, consist prefere` ably oi thin plates of spring brass or bronze which are cadmium or tin plated to facilitate the soldering or electrical connections thereto. These plates are each provided with an aperture of greater diameter than the aperture in the base The strips of dielectric material 2E in ythe 'form oi thin sheets of some good insulati.' g material, such as ruby India mica, etc. These strips also provided with apertures 26 or diameter corresponding to that of the base aperture The pressure plat-e 22 is made from a metallic plate, preferably of brass, which is cadmium or tin plated. This plate 22 is een# siderably thicker than the condenser plates 2li. The plate is provided with a central aperture 2l the walls oi' which are extended during the punching operation so that internal threads 23 may be provided for engagement therewith oi the threads on the adjusting screw 2li.

The walls il and l2 defining the open ended cavity in the base member are provided with oppositely disposed bosses or ribs 28 (Fig. l). These bosses or ribs serve to properly align the condenser elements relative to the cavity and relative to the base aperture I5. To further this aim, the plates 20 are so constructed that recesses 30 are provided at one end of each plate While the other end is provided with a recess 3l and an opposite recess 32, partially formed by an ear 34. These recesses 30, 3l and 32 are so positioned as'to substantially engage portions of the ribs or bosses 28. Since the major por tion of each plate 20 is of less Width than the width of the cavity dened by the walls Il and I2, spacing members are formed on the edges of the plates to assure that the plates will t properly between these walls. As shown in Fig. 4 the plate 20 is provided near one end with ears 35 and near the other end with ears 36. These ears 36 are closer to their respective end of the plate than the ears 35 are to their end of the plate. The purpose of this construction is to assure that the ears of one plate will not be directly aligned with the ears of another plate of the condenser assembly, it being understood that one plate of the assembly will be in reversed position relative to another plate in the assembly. A suitable terminal member 31 extends upwardly from one end of the plate 20.

The strips of dielectric material 2| have their ends provided with concavities 38 to engage portions of the ribs or bosses 28. The pressure plate 22 has its ends provided with concavities 39 spaced from the bosses 28. This pressure plate 22, however, is a slight bit shorter than the condenser plate '2U so that when the device is assembled the possibility of an end of the pres-- sure plate contacting with the terminal 3T is substantially prevented.

The condenser unit is assembled substantially as follows: A condenser plate 20 is positioned in the cavity of the base with the undersuriace or the plate 2li resting fiat against the bottom ci the cavity. A strip oi dielectric material 2l is then placed directly over the top surface ci the plate 2li. A second plate 2l is placed on 'top of the irst strip of dielectric material 2i. Since it is desired that the condenser be adjustable, this second plate is bowed substantialH throughout its length so that when no pres-AA sure is applied to this upper plate the upper plate is separated from the strip of dielectric material throughout the major portion oi its length. A. second strip of dielectric material El is then positioned on top of the top plate 2t and the pressure plate is then positioned to everlie this upper strip oi' dielectric material With these parts in this position., proper alignment being assured by the various recesses in the members engaging the ribs. or bosses 28, they may be` locked in position by means of the adjusting screw which passes through the base aperture through the apertures 25 and 2B, into threaded engagement with the wall oi the pressure plate aperture This adjusting screw 2f;- can be turned until the condenser unit is in a condition shown in lig. 3, wherein the 'upper plate iid is hattened out firmly against the lower dielectric strip 2l. In this condition the condenser has its maximum capacity. Ol course the screw 2li can be turned to permit the bowed upper plate 26 to 'den and separate throughout the major portion of its length relative to the lower plate, the amount of bow in this upper plate determining the capacity of the condenser, 'which decreases as the upper plate becomes more separated from the lower plate. Since plates 26 and 26 are in opposite positions as indicated by their respective terminals 31 and 3l', it will be apparent that the spacing ears 35 and 36 of the respective plates will be in staggered relation. Thus these plates are definitely locked in the cavity, and at the same time the spacing e-ars are out of register so that chances of one plate coming in direct Contact with another plate are prevented. The provision of the upstanding Walls Il and l2 assures that with the plate arrangement shown the plates will not be capable of any substantially shifting of position during adjustment, and, moreover, these upstandlng walls serve admirably to protect the edges` of the relatively fragile strips o1" dielectric material, it being understood that these strips are of such width as to extend beyond the major portion of the various condenser plates. i

,A condenser constructed and assembled as just described possesses all of the advantages set forth hereinbefore, namely, the condenser is adjustable with a minimum of drift of capacity change due to temperature or humidity changes; the edges of the dielectric material are protected by the cavity walls; the various elements of the unit are denitely positioned in the cavity; and the unit possesses adjustability Within desired ranges. While the desired assembly has been shown as being constructed simply of a pair of plates 20 land 20', it should be understood that additional plates similar to plate 20 can be applied in the assembly in the event it is desired to increase the capacity of the unit in which event the additional plates would be connected electrically alternately to the plate 20 and plate 20. Each additional plate will be bowed, of course, and each additional plate will be insulated from the other elements by similar strips of dielectric material similar to strip 2|. The prevention of drift or capacity change can be aided by connecting the unit in a suitable circuit in such fashion that the plate 20 is connected to be at low potential.

While the base I0 just described has been illustrated as having therein a single cavity for a condenser unit, the base may be constructed to have a plurality of cavities for the reception of a plurality of condenser units so that the device may assume the form of a gang or multiple condenser assembly. In Figs. '7 and 8 the base 50 is provided with Walls 5| and 52 dening one cavity and with Walls 54 and 55 dening another cavity. A condenser unit A is shown positioned in the cavity denedby the walls 5| and 52, while a similar unit B is shown in the cavity defined by the walls 54 and 55. The walls 5|, 52, 54 and 55 are constructed entirely in accordance with .the walls I and I 2 and the Various elements of the condenser elements A and B correspond to the various elements shown in Figs. 1 to 6, inclusive. It should be understood, of course, that any number of plates can be used in these umts A and B to obtain the desired capacity range. The other side of the base 50 is provided With an enlarged recess 56, the ends of which are arcuate shape as at 5l for the reception of a rounded end strip of metal 58. This strip of metal is provided with apertures through which the shanks of adjusting screws C and D may pass, so 'that the heads of these screws will bear against the exposed surface of the strip. The

strip is also provided with an aperture 59 inalignment with the central aperture 60 of the base. 'I'he base may be provided with additional apertures 6| if desired.

The aperture 59 is provided in the strip 58 (the strip 58.`being preferably of cadmium plated brass) for the passage of any suitable member or stud for attaching the gang condenser assembly, either to a shield or to any other grounded member of a receiving set or to even a grounded conductor. The shield or chassis of the set can be grounded so that the adjustment screws C and D are in ground potential. Thus the gang condenser is effectively and electrostatically shielded in that the adjustment screws are at ground potential, permitting the use of a. metal adjusting tool without causing such detuning of the circuits in which the condensers are used as normally occurs due to the body capacity of the one adjusting the condensers.,

An illustration of the manner in which the gang condenser of Figs. '7 and 8 can be used with other parts of a receiving set is shown clearly in Figs. 11 and 12 wherein a threaded rod or studY 'I8 having a nut 1| immovably secured intermediate the ends thereof passes through the opening 59 of the plate 58, through the opening 60 into the threaded bore 'l2 of a rod of insulating material 14 on which the inductances 15 of a transformer unit can be wound. The threaded portion 16 of the rod l0 extending beyond the nut 1| may be used to secure the transformer unit in a shielded can or to any other suitable part of the chassis. A simple nut will suilice to make this installation. It should be understood,

of course, that the shielded can or other support will have apertures aligned with the heads of the adjusting screws C and D for the passage of a suitable tool utilized in adjusting the respective condensers A and B.

In the modification shown in Figs. 9 and l0, a base 8| is provided with walls 82, 84, 85, 86, 8l and 88: the pair of walls 82 and 84 deiining a cavity for the reception of a condenser unit E; the pair of Walls and 86, defining a cavity for the reception unit F; and the walls 8l and 88 defining a cavity for the reception o-f a condenser unit G. The construction of the Various walls and of the condenser units is similar to the constructions heretofore described. A metallic bar similar to the bar 58 is positioned in a recess 9| in the opposite surface of the base 8|, such bar 90 being provided with apertures for the passage of the shanks of adjusting screws H, J and K associated with the respective units E, F and G. Rods or studs similar to the rod 10 pass through openings in the bar 90 and in the base 8| so that the nut portion 94 of each stud is fastened securely against the upper surface of the bar 90. The shank portion of these rods may be engaged by nuts on the cavity side of the base 8|. The corresponding-portions 98 of the rods or studs may be used to attach the gang condenser assembly to a suitable shield or other support, which preferably, can be grounded. Thus a good electric connection between the various adjusting screws H, J and K is provided, and if this bar 90, which provides the connection is grounded, it is possible to adjust the capacity of any one or all of the condensers E, F, or G without causing such detuning of the circuit with fir which the condenser is associated as normally f occurs due to the body capacity of the one adjusting the condenser.

While the gang condenser assemblies have been shown embodying assemblies of two and three units, it will be apparent that the number of units in a gang assembly can be increased as occasion may demand. In any form of gang assembly, the present invention provides an arrangement in which adjusting screws can be kept at grounded potential thereby facilitating adjustment Without interfering with the characteristics of the circuits including the condensers. Moreover, the form of base shown aids in preventing stray capacities between the units of a multiple condenser assembly. Also if the low potential plate is positioned adjacent the insulating material of the base, such stray capacities are further minimized.

While the cavities shown in the various embodiments of the invention have been shown and described as being substantially open ended, it is to be understood that the invention is not to be limited to such arrangement. The open ended cavities are provided to facilitate the attachment of conductors to the plate terminals, but it is contemplated that these cavities could have end Walls as well as side Walls.

I claim:

1. A device of the character described comprising a molded base of insulating material having a plurality of cavities therein, a condenser unit in each of said cavities, individual adjusting members for varying thecapacities of said units, and a single member secured to said base and. electrically connected to said adjusting members whereby all of said adjusting members can be grounded with a single ground connection.

2. A device of the character described comprising a molded base of insulating material having a plurality of cavities therein, a condenser unit in each of said cavities, individual adjusting screws passing through said base and cooperating with a pressure plate in each condenser unit for varying the capacity of said units, and a bar secured to said base and having apertures therein through which said adjusting screws pass to electrically connect all oi said adjusting screws.

3. A device of the character described comprising a molded base of insulating material having a plurality of cavities therein, a condenser unit in each of said cavities, individual adjusting to serve as a common ground connection to 10 ground all of said adjusting screws.

LYMAN G. KETCHAM. 

